The derma roller? It's a cool tool, but seriously, it's more beneficial to use it once every three months or so, if it's a decent product. Of course needle size makes a difference as well. But with derma rolling; less will be better. It's a shock to the system, makes your body produce more of collagen etc..
Disinfectant doesn't cost much! Hydroperoxide 3 % isn't expensive and there are other good disinfectants available as well. Want to keep your skin in order? Sanitize that tool and don't use it too often!
There are better creams, those high in vitamin E etc., to use after derma rolling.
Boiling / very hot water can do a lot in terms of disinfecting, warm won't. I find it easier to buy some sanitizer and let the roller soak in the solution for a while.
Probably your diet is in order, but it's good to include good oils and lots of water, to keep the skin moisturised.
Lycka till! (From Finland, and from a Finnish guy.)